Torsional vibrations occur in motor vehicles having an internal combustion engine, in particular at low engine speeds, which cannot always be damped adequately by a dual-mass flywheel situated in the drivetrain.
In dual clutch transmissions, as a rule two transmission lines are available within the transmission. Each transmission line can be activated by means of a respective clutch to transmit torque when the relevant clutch assigned to the transmission line is engaged, in order to be able to transmit an intended torque when a gear ratio is selected. The clutch of the other, inactive transmission line remains disengaged in this case. A gear ratio may be selected in the inactive transmission line, however, in order to be able to achieve a faster transmission ratio change by means of gear pre-selection.
Torsional vibrations occur, in particular, in three-cylinder engines at low speeds of rotation. In dual-clutch transmissions, resulting in vibrations in the free play of the coupled but inactive transmission line or the inactive input shaft, because the angles of oscillation of the secondary mass of the dual-mass flywheel are still too large.
It would of course be possible to avoid vibration by pre-selecting neutral for the inactive transmission line and the inactive input shaft. However, this results in increased shifting times when changing the transmission ratio, because the subsequent gear ratio still has to be selected first, which is very disruptive, in particular at low speeds of rotation. The preceding arrangement is also very disadvantageous, because the driving conditions in question occur especially frequently in city traffic.
Rattling sounds in the drivetrain are eliminated in the existing art according to DE 10 2006 008 207 A1 by engaging the clutch of the passive transmission line in such a way that slippage develops at the clutch, so that the passive transmission line comes under load and slight tension and the parts of the transmission line bear against each other due to the tensioning, so that even if there are vibrations little or no rattling can be heard.
However, the above method has the disadvantage that the continuously slipping application of the clutch results in substantial wear to the clutch, and also in unacceptably high increased fuel consumption.
The object of the invention is therefore to create a method for controlling a transmission which achieves a reduction or suppression of vibrations of transmission elements and/or of rattling sounds, and yet causes little wear and only slight but acceptable increased fuel consumption.